The present invention relates in general to semiconductor power devices, and in particular to an apparatus and method for a dual gate low impedance power switch which enables accurate current sensing and has improved thermal dissipation characteristics.
Advances in power device technology have resulted in power transistors, such as MOSFETs and IGBTs, having very low drain to source resistance or RDS(ON). A low RDS(ON) is desirable, because it allows higher current drive and lower heat dissipation thus resulting in reduced power loss in the power transistor.
Current sense schemes are used to detect the current through the power transistor to prevent permanent damage. Sense amplifiers used to detect the current through power transistors typically have an offset error. For the sense amplifier to accurately sense the current through the power transistor, the signal that is being sensed needs to be sufficiently greater than the offset error of the amplifier so that the sense amplifier can accurately measure the current through the power transistor. However, with substantially reduced RDS(ON), the voltage drop across the power transistor has reduced to such degree that the amplifier offset voltage has become a significant percentage of the voltage drop across the power transistor, thus compromising the ability of the amplifier to accurately sense the current through the power transistor. Attempts have been made to design amplifiers with low offset voltages, but these amplifiers are complex and costly.
Thus, there is a need for a technique that enables accurate measurement of the current through low impedance power transistors without the need for complicated sensing circuitry.